ALLOW

Treatment tested

• Peginterferon beta-1a

  Interferon alpha/beta receptor agonist

• Naproxen

  Cyclooxygenase inhibitor

Other measures (30)

Key Inclusion Criteria: * Must have a confirmed diagnosis of relapsing forms of multiple sclerosis (MS), as defined by McDonald criteria #1-4 [Polman 2005] * Must have neurological findings consistent with an Expanded Disability Status Scale (EDSS) score of 0.0 - 5.0 * Must be treated with IFN-β and must be receiving a stable dose of IFN-β for at least 4 months immediately prior to screening * All male patients and female patients of childbearing potential must practice effective contraception during the study and be willing and able to continue contraception for 3 months after their last dose of study treatment. Key Exclusion Criteria: * Primary progressive, secondary progressive, or progressive relapsing MS [Lublin and Reingold 1996]. These conditions require the presence of continuous clinical disease worsening over a period of at least 3 months. Patients with these conditions may also have superimposed relapse but are distinguished from patients with relapsing MS by the lack of clinically stable periods or clinical improvement * History of severe allergic or anaphylactic reactions or known hypersensitivity to medication which might suggest potential for a reaction to IFN β-1a or polyethylene glycol * History of malignant disease, including solid tumors and hematologic malignancies (with the exception of basal cell and squamous cell carcinomas of the skin that have been completely excised and are considered cured) * History of seizure disorder or unexplained blackouts OR history of a seizure within 3 months prior to Baseline * Known allergy to any component of the BIIB017 formulation * An MS relapse that has occurred within the 50 days prior to Baseline (Day 1) and/or lack of stabilization from a previous relapse prior to Baseline. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

The primary objective of this study is to determine the proportion of participants with relapsing multiple sclerosis who experience new and/or increased flu-like symptoms (FLS) after transitioning from nonpegylated IFN-β therapies to peginterferon beta-1a (BIIB017). Secondary objectives are: to determine the severity and frequency (measured by flu-like symptom score [FLS-S]) of FLS in these participants; to determine the duration (measured in number of hours) of FLS in these participants; to determine the effect of BIIB017 on other participant-reported outcomes, including treatment satisfaction (measured with the Treatment Satisfaction Questionnaire for Medication [TSQM]) and disability status (measured with the Patient Determined Disease Steps [PDDS]) over a 56-week period; to determine whether interferon-related FLS result in missed days of work/daily activities (e.g., absenteeism); to assess the use of additional medications (in addition to current medications used to treat FLS) to relieve BIIB017-related FLS; to determine the incidence of adverse events throughout the study period; to characterize the immunogenicity profiles of participants switching from prior IFN-β therapy to BIIB017.